Detection of short circuits in a vehicle

ABSTRACT

The invention relates to a method and an arrangement for the detection of shorts circuits in the electrical system in a vehicle provided with a battery comprising—measuring and storing the value of the battery voltage at a first moment in time,—measuring the value of the battery voltage at a second moment in time,—comparing the values of the battery voltage at the first and second moments in time,—checking, if the battery voltages at the two moments in time differ from each other by more than a predetermined value, whether one or several of certain predefined systems in the vehicle have been engaged during the interval of time between the first and the second moments in time, with a short circuit being assumed to have taken place if none of the systems in the vehicle have been engaged during the interval of time.

The present invention is a continuation of International Application No.PCT/SE2004/001195, filed Aug. 16, 2004, which claims priority to SE0302512-9, filed Sep. 18, 2003, both of which are incorporated byreference.

BACKGROUND AND SUMMARY

The present invention relates to a method and an arrangement fordetection of short circuits in a vehicle. By means of the invention,short circuits in a vehicle can be detected in a simple and reliable wayand can accordingly be remedied.

In modern vehicles, such as, for example, trucks, buses and constructionvehicles, there is a very large amount of electrical cabling. Due to,for example, incorrect laying of cables and movements of the vehicle,the cables' insulation can be damaged, whereby short circuits can arise.These short circuits can be of short duration and intermittent, whichmeans that the fuses in the vehicle are not able to react, which can bevery trying and irritating for the driver of the vehicle. In addition,various electrical systems in the vehicle can be disturbed by a shortcircuit of short duration, with an error function as a result. Forexample, a processor in a control unit can restart when the supplyvoltage drops below a certain level.

To be able to detect short circuits in a vehicle reliably at an earlystage is therefore an important function in a vehicle.

Document JP 11055848 describes an arrangement that is intended to detectshort circuits in the electrical system in a car. A disadvantage of thisarrangement is that it can only detect short circuits on the specificcable to which it is connected.

It is desirable to produce an arrangement and a method for being able todetect short circuits that are of short duration and/or intermittent inthe electrical system in a vehicle, suitably a truck, at an early stagein a quick and reliable way.

In accordance with an aspect of the present invention, a method isprovided for detection of short circuits in the electrical system in avehicle provided with a battery. The method comprises measurement andstorage of the value of the battery voltage at a first moment in time,measurement of the value of the battery voltage at a second moment intime, and comparison of the values of the battery voltage at the firstand second moments in time.

If the battery voltages at the two moments in time differ from eachother by more than a predetermined value, it is checked whether one orseveral of certain predefined systems in the vehicle have been engagedduring the interval of time between the first and the second moments intime, with a short circuit being assumed to have occurred if none of thesystems in the vehicle have been engaged during the interval of time.

In a further aspect of the invention, an arrangement for carrying outthe method steps as described above is provided.

The method is suitably carried out continually while the vehicle isoperation, and in the same way, an arrangement according to theinvention can be running and carrying out measurements and comparisonscontinually while the vehicle is in operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail in the following, withreference to the attached drawings, in which:

FIG. 1 shows the voltage level in a vehicle during a short circuit ofshort duration,

FIG. 2 shows a comparison according to the invention, and

FIG. 3 shows an additional comparison according to the invention.

DETAILED DESCRIPTION

FIG. 1 shows schematically the battery voltage level in a vehicle duringa temporary short circuit in the electrical system in the vehicle. Atthe moment in time t1 when the short circuit occurs, the battery voltagedrops from a normal level Vnorm to a lower level V1, with the differencebetween the two levels being represented by ?V. After a little while,the short circuit has ceased, which means that at the moment in time t3the battery voltage returns to the normal level Vnorm. The fact that thebattery voltage returns to its normal value can also be due to thevehicle's generator managing to compensate for the drop in voltage ?Vduring a short circuit of longer duration.

According to the invention, this temporary drop in battery voltageduring a short circuit of short duration is used to detect shortcircuits that are of such a short duration that the vehicle's fusesand/or other systems in the vehicle are not able to react to them.

The fact the battery voltage in the vehicle drops for a brief intervalof time can also be due to other causes that must be taken intoconsideration so that incorrect detections of short circuits do notoccur. The most probable alternative reason for a drop in batteryvoltage similar to one that is caused by a temporary short circuit isthat a consumer of electricity, in other words a subsystem in thevehicle, has been engaged. Examples of such subsystems areair-conditioning systems, climate-control systems, lighting, audio, etc.

In the event of the engaging of a subsystem that consumes energy, thebattery voltage will drop momentarily, after which the vehicle'sgenerator cuts in and returns the battery voltage to its normal level,Vnorm. This sequence is very similar to the one that occurs during ashort circuit of short duration. It will be described in greater detail,below in this description, how it is possible, according to theinvention, to distinguish between these two different causes of a dropin voltage.

FIG. 2 shows an outline drawing of the underlying idea behind theinvention. A control unit, an ECU (Electronic Control Unit), in avehicle measures, or obtains from separate measuring equipment in thevehicle, the value V(t1) of the battery voltage in the vehicle at afirst moment in time t1. This value of the battery voltage is stored andlater compared with the value V(t2) of the battery voltage at asubsequent second moment in time t2. The value for the moment in time t2is suitably the actual value of the vehicle's battery voltage at thetime of the comparison, but can also be a stored value from anothermoment in time that differs in time from t1. If V(t2) differs from V(t1)by a certain predetermined minimum value, the ECU will assume that ashort circuit has taken place. The size of this minimum difference valuecan, of course, vary between different types of vehicle and differentmodels, but a suitable value for the difference is of the order of 200mV or more for a vehicle with a system voltage of 28 Volt. The timebetween the two measurement values V(t1) and V(t2) that are comparedwith each other can, of course, also vary depending upon theapplication, but can suitably be of the order of 1-10 ms, which thuscorresponds to the frequency at which a comparison is made. As mentionedabove, the comparison can suitably be carried out continually while thevehicle is in operation.

Short circuits that are of the duration that has been mentioned, inother words of the order of fractions of a second, will scarcely benoticed by the driver, but can still constitute important informationfor an inboard computer, as short circuits caused by, for example,damaged insulation around cables tend to become worse with time. Theinboard computer, the ECU, or some other function in the vehicle thatreceives information from the ECU can utilize the information concerningshort circuits that are of short duration and/or intermittent toinvestigate whether the number of such short circuits increases. Such anincrease can, in turn, be used by the inboard computer or anothersimilar function in the vehicle to warn the driver or to recommend tothe driver that troubleshooting should be carried out.

FIG. 3 shows a more detailed outline block diagram of an arrangementaccording to the invention. As with the arrangement in FIG. 2, aninboard computer, ECU, or the like in the vehicle is provided with theability to obtain the value V(t1) of the battery voltage at a firstmoment in time t1, which value has been measured at the moment in timet1, and has been stored, and also to obtain the value of the batteryvoltage V(t2) at a subsequent second moment in time t2.

As mentioned above, the connecting in of various subsystems in thevehicle that consume electricity can cause a drop in voltage similar tothe one that is caused by a short circuit. Therefore, if the ECU detectsa difference between V(t1) and V (t2) concerning amplitude and extent intime that indicates a short circuit, the ECU carries out a statuscontrol of certain predefined subsystems in the vehicle. Examples ofsuch subsystems have been given above, for example lights, audio,air-conditioning, climate-control, etc. These subsystems are such thatthey draw a lot of current and therefore produce a drop in voltage thatresembles a temporary short circuit.

The status control that the ECU carries out is that it stores in amemory information concerning which of the predefined subsystems areconnected in or disconnected. If the ECU has information to the effectthat one or several of the subsystems have been engaged at a moment intime that lies between t1 and t2, it is assumed that no short circuithas taken place.

In the present application, the use of terms such as “including” isopen-ended and is intended to have the same meaning as terms such as“comprising” and not preclude the presence of other structure, material,or acts. Similarly, though the use of terms such as “can” or “may” isintended to be open-ended and to reflect that structure, material, oracts are not necessary, the failure to use such terms is not intended toreflect that structure, material, or acts are essential. To the extentthat structure, material, or acts are presently considered to beessential, they are identified as such.

The invention is not restricted to the embodiments described above, butcan be varied freely within the framework of the attached patent claims.

1. A method for the detection of short circuits in the electrical systemin a vehicle provided with a battery, comprising: measuring and storinga value of a battery voltage at a first moment in time; measuring andstoring a value of the battery voltage at a second moment in time;comparison of the values of the battery voltages at the first and secondmoments in time; and generation of a message if the battery voltages atthe two moments in time differ from each other by more than apredetermined value.
 2. The method as claimed in claim 1, comprisingcarrying out the method continually while the vehicle is in operation.3. The method as claimed in claim 1, comprising checking, if the batteryvoltages at the two moments in time differ from each other by more thana predetermined value, whether at least one of certain predefinedsystems in the vehicle have been engaged during an interval of timebetween the first and the second moments in time, and assuming that ashort circuit has taken place if none of the systems in the vehicle havebeen engaged during the interval of time.
 4. The method as claimed inclaim 3, comprising carrying out the method continually while thevehicle is in operation.
 5. An arrangement for detection of shortcircuits in an electrical system in a vehicle provided with a battery,comprising: means for measuring and storing a value of the batteryvoltage at a first moment in time; means for measuring the value of thebattery voltage at a second moment in time; means for comparing thevalues of the battery voltage at the first and second moments in time;and means for generating a signal, if the battery voltages at the twomoments in time differ from each other by more than a predeterminedvalue.
 6. The arrangement as claimed in claim 5, comprising means forchecking, if the battery voltages at the two moments in time differ fromeach other by more than a predetermined value, whether at least one ofcertain predefined systems in the vehicle have been engaged during aninterval of time between the first and the second moments in time, themeans being adapted to generate a signal indicating a short circuit ifnone of the systems in the vehicle have been engaged during the intervalof time.
 7. The arrangement as claimed in claim 5, wherein an electroniccontrol unit comprises at least one of the measuring means, thecomparing means, and the signal generating means.